A plastic optical fiber (hereinafter merely referred to as an “optical fiber”) has already been put into practical use in applications such as short-distance data communication and sensing. It that case, an optical fiber is rarely used alone. The optical fiber is often used in the form of an optical fiber cable after protecting whose outer periphery is protected with a covering layer.
To enhance the heat resistance and the durability to chemicals of such an optical fiber cable, techniques of using a polyamide polymer as the covering layer are proposed in Japanese Unexamined Patent Application, First Publication No. Hei 10-319281, Japanese Unexamined Patent Application, First Publication No. Hei 11-242142, Japanese Unexamined Patent Application, First Publication No. Hei 10-332995, and Japanese Unexamined Patent Application, First Publication No. Hei 10-307218.
With respect to the optical fiber cable used within doors such as automobiles and factories, flame resistance is required. To reduce a toxic gas evolved during combustion, there is required an optical fiber cable which is free from halogen and is also superior in flame resistance. In “Polyamide Resin Handbook” (published by THE NIKKAN KOGYO SHIMBUN, LTD., written by Osamu FUKUMOTO), a technique of mixing a triazine compound, especially melamine or melamine cyanurate, with a polyamide polymer is proposed.
However, an optical fiber cable using the polyamide polymer as the covering layer had such drawbacks that the flexural modulus is high, winding tendency remains when stored in the state of being wound around a bobbin or the like, and the handling property is poor when formed into an optical fiber cable assembly such as wire harness and an optical fiber cable with a plug. Furthermore, when the triazine compound is introduced into the polyamide polymer to enhance the flame resistance, the flexural modulus is further increased and the handling property is especially poor.